Catalyst solution for electroless metal deposition on a substrate

ABSTRACT

The invention disclosed herein is a catalyst for activating a substrate prior to electroless metal plating and to a process for making the same. The catalyst comprises the product resulting from the admixture of an acid soluble salt of a catalytic metal, a stannous salt, an acid and an extraneous source of halide ions. The extraneous source of halide ions provides an excess of halide ions in the catalyst formulation over that found in prior art formulations. The catalyst differs from prior art catalysts in the excess of halide ions and is an improvement as it may be used at a higher pH to catalyze substrates normally attacked by strong acids, is more stable and is adsorbed onto substrates to a greater extent than prior art catalysts.

United States Patent Gulla et al. Sept. 9, 1975 [54] CATALYST SOLUTIONFOR ELECTRQLESS 3,672,938 6/1972 Zeblisky 1 17/47 A METAL DEPOS T ON ASUBSTRATE 3,764,488 10/1973 Bernhardt 204/38 B [75] Inventors: MichaelGulla, Newton; William A.

Conlan, Jr., Attleboro, both of Mass.

[73] Assignee: Shipley Company, Inc., Newton,

Mass.

[22] Filed: June 27, 1973 21 Appl. No.: 374,093

Related us. Application Data [63] Continuation-impart of Ser. No.224,742, Feb. 9,

1972, abandoned.

[52] US. Cl 427/304; 106/1 [51] Int. Cl. B44D 1/092 [58] Field of Search117/213, 47 R, 47 A, 71 R,

117/130 E, 138.8 R, 160 R; 106/1 Primary Examiner-Thomas .1. Herbert,Jr. Assistant Examiner--Bruce H. Hess Attorney, Agent, or Firm-Robert L.Goldberg 5 7 ABSTRACT The invention disclosed herein is a catalyst foractivating a substrate prior to electroless metal plating and to aprocess for making the same. The catalyst comprises the productresulting from the admixture of an acid soluble salt of a catalyticmetal, a stannous salt, an acid and an extraneous source of halide ions.The extraneous source of halide ions provides an excess of halide ionsin the catalyst formulation over that found in prior art formulations.The catalyst differs from prior art catalysts in the excess of halideions and is an improvement as it may be used at a higher pH to catalyzesubstrates normally attacked by strong acids, is

[ References Cited more stable and is adsorbed onto substrates to aUNITED STATES PATENTS greater extent than prior art catalysts.

3,011,920 12/1961 Shipley 117/213 3,379,556 4/1968 Chiecchi 117/47 A 59Clams 2 Drawmg F'gures Sn CONCENTRATION I A= A'= 0.05 moles 11m B=a'=o.13 u H TOTAL CHLORIDE CONCENTRATION (moles) 4s CATALYST SOLUTIONFOR ELECTROLESS METAL DEPOSITION ON SUBSTRATE name of Michael Gulla andWilliam A. Conlan on Feb. 1

9, 1972, now abandoned.

BACKGROUND OF THE INVENTION 1. Introduction This invention is directedto a formulation for catalyzing a substrate prior to electroless metaldeposition.

2. Description of the Prior Art For electroless plating of substrates,especially for the plating of non-conductive substrates, it has beenknown for some time that chemically plated metal deposits of suitablethickness and adequate bond strength are commercially practical only ifthe substrate surface is properly catalyzed prior to metal deposition.

A common method for catalyzing a substrate prior to plating involvescontact of the substrate with two solutions known in the art as atwo-step catalyst. A process for metallizing utilizing this catalystcomprises contact of a substrate with a first aqueous solution ofareducing agent such as stannous chloride followed by contact with asecond solution of a catalytic metal salt such as palladium chloride inhydrochloric acid. The reducing agent reduces the catalytic metal saltin situ on the substrate surface to the catalytic metal therebyproviding a catalytic surface receptive to electroless metaldeposition-thereon. This procedure is employed successfully in manyplating-on-plastic applications. However, it is subject to variousdisadvantages including poor adhesion between the substrate surface anda subsequently applied metal deposit. This is especially true wherecopper is to be deposited over copper such as in the manufactue ofprinted circuit boards where copper is deposited over both a plasticsubstrate and a copper cladding over said plastic substrate. Also,articles in the process of being plated using the aforesaid twostepcatalyst must be re-racked subsequent to catalysis before proceeding toadditional steps in the plating sequence to avoid contamination of thecatalyst through dragin from preceding steps and rapid deterioration ofthe plating bath. Metal plate obtained using the twostep catalystexhibits stardustingi.e. minor imperfections on the surface of the metalplate.

An alternative method for catalyzing a substrate prior to electrolessdeposition is also known and is disclosed and claimed in U.S. Pat-No.3,01 1,920 incorporated herein by reference. In this method, a substrateis contacted with a colloidal catalytic solution formed by the admixturein acid solution of a catalytic metal salt, a stannous salt in molarexcess of the catalytic metal salt and a hydrohalide acid. The catalyticmetal may be selected from the group of silver, gold and the platinumfamily of metals. Palladium is the preferred catalytic metal. The excessstannous salt is believed to be responsible for stability of the colloidand prevents it from falling out of the formulation. The catalystoperates as a pH below about I and preferably well below 0. Thelimitation on the pH is due to the fact that the stannous salthydrolyzes and precipitates at a pH of about 0.9.

Though this colloidal catalyst has been widely ac- .cepted and preferredfor most applications, it is not without some difficulties. One suchdifficulty is that the highly acidic formulation attacks varioussubstrate materials, especially plastic materials including the plasticracks used to carry the substrate through the plating sequence. Anotherdifficulty is the volatilization of the hydrohalide acid which isundesirable from both 'a health standpoint and a quality controlstandpoint. Both of these problems could be overcome if the catalystformulation could be prepared at a higher pH.

In U.S. Pat. No. 3,672,938, there is disclosed a process catalyzing asubstrate prior to electroless metal deposition with a catalyst alsoformulated by the admixture in acid solution of a catalytic metal salt,a stannous salt in molar excess of the catalytic metal salt and ahydrohalide acid. This catalyst is said to differ from the catalyst ofU.S. Pat. No. 3,01 1,920 in physical form, it being asserted that thecatalyst of said patent is a true solution catalyst" rather than acolloidal catalyst as in the aforesaid U.S. Pat. No. 3,01 1,920.Regardless of its physical form, it is also highly acidic and suffersthe same disadvantages as the catalysts of said U.S. Pat. No. 3.011.920.

Attempts have been made in the prior art to formulate a low acid, higherpH catalyst. Such attempts have been unsuccessful because the low acidcatalyst has been formulated by the expedient of reducing thehydrohalide acid content. Such a reduction results in the formation of aprecipitate at a pH of about 0.9 for a chloride system. This formationof precipitate is believed to be due to hydrolysis of the stannous ionwith the formation of insoluble hydrolysis products. This results inloss of the catalyst. An example of this is shown in the aforesaid U.S.Pat. No. 3,672,938, Example V. where there is disclosed a catalysthaving a total acid content of one milliliter of concentratedhydrochloric acid per liter of solution. This formulation is of no commercial value as it is impossible to solubilize the stan nous salt andconsequently, a stable colloid or catalyst in any other form cannot beprepared.

DEFINITIONS The following definitions are provided to assist in theunderstanding-of the ensuing text:

Catalyst formulation is the product resulting from the admixture of anacid soluble salt of a catalytic metal, a stannous salt in molar excessof the catalytic metal salt, an acid and an extraneous source of halideions.

Catalyst component" refers to any one or more of the salts of thecatalytic metal, stannous salt or acid used in making the catalystformulation.

Actual halide ion concentration is the concentration of the halide ionsin the catalyst formulation if any of the catalyst components are usedin the form of a halide. This will be Zero if none of the aforesaidcomponents are used in the form of a halide.

Maximum component halide ion concentration" is the concentration ofhalide ions that would be in the catalyst formulation if each of thecatalyst components were usedin the form of the halide.

Total halide ion concentration is the required amount of halide ions inthe catalyst formulation in accordance with this invention.

, Extraneous halide ions and like terms mean a source of halide ionsother than iodide ions in addition to those supplied by the catalystcomponents. The concentration of the extraneous halide ions is equal tothe difference between the total halide ion concentration and the actualhalide ion concentration.

Excess halide ions" are halide ions in the catalyst in excess of themaximum component halide ion concentration and the concentration of theexcess halide ions is equal to the difference between the total halideion concentration and the maximum component halide ion concentration.The concentration of the excess halide ions equals the concentration ofthe extraneous halide ions when all of the catalyst components used tomake the catalyst are in the form of the halide.

Precipitation point" is the pH at which a precipitate forms in thecatalyst formulation rendering the catalyst unsuitable for use. Thisprecipitate is believed to be hydrolysis products of the stannous salt.

SUMMARY OF THE INVENTION The catalysts described herein are improvementsover catalysts such as those described and claimed in the aforesaid U.S.Pats. Nos. 3,01 1,920 and 3,672,938 in that they have greater solutionstability, better absorption properties and, if desired, a decreasedhydrogen concentration with a correspondingly higher pH.

The invention is predicated in part upon the discovery that the halideions play a significant role in the functioning of the catalyst and thatthe catalyst is improved when the concentration of the halide ions isincreased beyond that concentration found in prior art catalysts by theaddition of an extraneous source of halide ions. The improvementsresulting from excess halide ions comprise improved stability andadsorption properties and solubilization of the stannous salt orretardation of the precipitation point. Accordingly, catalysts ofincreased pH can be formulated thereby providing catalysts suitable foruse with materials readily attacked by strong acids.

A catalyst composition in accordance with this invention comprises theproduct resulting from the admixture of( l an acid soluble salt of acatalytic metal, (2) a solution soluble stannous salt in molar excess ofthe catalytic metal salt, (3) an acid and (4) an extraneous source ofhalide ions in an amount sufficient to provide an excess of halide ionsin the formulation. The catalyst formulations of this invention have apH of less than about 3.5 dependent upon the stannous content as will beexplained in greater detail below.

DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 graphically represents precipitation point ofa series ofcatalysts as a function of pH; and

FIG. 2 graphically represents the precipitation point of a series ofcatalysts as a function of stannous ion concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The catalysts of this inventionare formulated substantially with materials and in proportions such asthose described and claimed in the aforesaid US. Pat. Nos. 3,01 1,920and 3,672,938. The acid soluble salt of the catalytic metal is a salt ofany of those metals known to exhibit catalytic properties in chemicalplating. Such metals include the precious metals, golld and silver andmembers of the platinum family. Palladium is generally found to be themost satisfactory of these catalytic metals for the activation of anon-conducting 4 substrate, particularly a plastic substrate, andtherefore constitutes the preferredembodiment of this invention. silver,gold and rhodium constitute lesser preferred embodiments of theinvention as some difficulty is encountered in the preparation of thecatalyst due to limited solubility of the salts of these metals insolution.

The particular salt of the catalytic metal used is not critical and maycomprise the halides such as those described in the aforesaid US. Pat.No. 3,01 1,920 as well as such other salts such as the nitrate, sulfateand the like. Salts other than halides are suitable as halide ions willbe introduced into solution by the extraneous source of halide ions.Preferably, the salt is the halide having an anion common to that of theother catalyst components. It should be noted that when the halide saltis used, some halide is introduced into solutions, but because of thelow concentration of the catalytic metalsalt used, this amount isgenerally negligible.

The amount of the catalytic metal salt is not critical and is primarilygoverned by cost and functional considerations. Thus, though up to 5grams per liter or more of the catalytic metal salt is possible, it isdesirable to maintain the quantity of the salt as low as possible from acost consideration without sacrificing the functional properties of thecatalytic formulation. Typically, the amount of the catalytic metal saltin a madeup bath does not exceed 2 grams per liter of solution and morepreferably ranges between about 0.1 and l gram per liter of solution.

The particular stannous salt used to formulate the catalyst is likewisenot critical and in addition to a stannous halide, other stannous saltsare suitable such as stannous nitrate and stannous acetate. As with thesalt of the catalytic metal, the stannous halide having an anion commonto that of other catalyst constituents is preferred. When a stannoushalide is used, a source of halide ions is introduced into the catalystformulation though this amount by itself does not provide sufficienthalide ions for purposes of this invention.

The amount of stannous salt used is not critical provided stannous ionsare present in the catalyst formulation in molar excess of the catalyticmetal ions. In this respect, as in the prior art, the molar ratio of thestannous ion to the catalytic metal ion may be as low as 2:1, butpreferably varies between 10:1 and 40:1 and may be as high as :1.

The hydrohalide acids, other than hydriodic acid, are preferred forpurposes of this invention. However, results in terms of stability andcatalytic activity with hydroflouric acid are marginal. Hydrobromic acidis better and hydrochloric acid provides the best result. Accordingly,the term hydrohalide acid as used herein is intended to mean principallyhydrochloric acid, but also. includes hydrohalide acids other thanhydriodie acid with the realization that these other acids provide onlymarginal results. It should be further realized that the termhydrohalide acid means the presence of hydrogen ions and halide ions insolution though the hydrogen ions may be derived from any other acidthat does not have an anion detrimental to the catalyst .formulation.Thus sulfuric acid, as an example, may be used as a source'of hydrogenions with all of the halide ions being supplied by the extraneous sourceof halide lOnS.

The amount of acid used may be substantially less than in thecommercially acceptable formulations of the prior art. In the prior art,the concentration of the acid had to be sufficiently high so as toprovide a catalyst having a pH of less than 1 and typically was so highas to provide a catalyst having a pH below 0. Using hydrochloric acid asan example, as much as 12 moles per liter of solution were used. Inaccordance with this invention, though such high concentrations of acidcan be used, the acid concentration can be reduced to a level wherebythe pH of the catalyst is as high as 3.5. Accordingly, for purposes ofthis invention, an operative range for the acid is from saturation tothat amount that results in a solution pH of 3.5 and in the preferredembodiment of the invention, the acid is used in an amount sufficient toprovide a pH ranging between 1 to 2.5. It should be noted that thoughcatalysts can be for mulated with a pH as high as 3.5, this isprincipally accomplished when the stannous ion concentration is relatively low. consequently, the stability of catalysts at this high pH isnot entirely satisfactory for storage of catalyst for long periods oftime.

From the above description, it can be seen that all of the catalystcomponentsi.e., the catalytic metal salt, the stannous salt and theacid, may or may not be used in the form of their respective halidesthough in a preferred embodiment of the invention, they are all halideshaving a common anion, most preferably chloride. With reference to thedefinitions set forth above, if all catalyst components were in the formof the halide, the resulting halide concentration, referred to as themaximum component halide ion concentration, would not be sufficientlyhigh to obtain the improvements in the stability and adsorptionproperties and the retarded precipitation point. Obviously, if one ormore of the catalyst components were used in a form other than thehalide, then the actual halide ion concentration would be lower than themaximum component halide ion concentration and still insufficient toobtain the improvements noted above.

In accordance with the invention described herein, an excess of halideions is provided in the catalyst formulation, above the maximumcomponent halide ion concentration, by the addition of an extraneoussource of halide ionsv The amount of the extraneous halide ions added isequal to at least the difference between the actual halide ionconcentration and the required total halide ion concentration.

In determining the required total halide ion concentration, differentconsiderations apply dependent upon whether the pH of the catalyst isbelow or above the precipitation point, the pH at which a precipitateformswhich precipitate is believed to be insoluble hydrolysis productsof tin.

With regard first to catalyst formulations having a pH below theprecipitation point in the absence of the extraneous halide ions, thetotal halide ion concentration required is not critical, it beingunderstood that the higher the total halide ion concentration, thegreater will be the stability and adsorption propertiesof the catalystthough the improvements in these properties are sometimes difficult toascertain, especially with those catalysts having a high hydrogen ionconcentration-e.g., a concentration such that the pH of the catalyst isbelow 0. In general. at a pH below the precipita tion point, the totalhalide ion concentration is at least 0.2 moles in excess of the maximumpotential halide ion concentration and preferably, at least 0.5 moles inexcess. The maximum concentration is not critical and the total halideion concentration can be at saturation. Accordingly, the range for thetotal halide ion concentration is from an excess halide ionconcentration of at least 0.2 moles to saturation and preferably atleast 0.5 moles to saturation. The concentration of the extraneoussource of halide ions is that amount necessary to increase the actualconcentration of the halide ions to the total concentration of halideions required as described above. Obviously, a greater amount ofextraneous halide ions will be required when one or more of the catalystcomponents such as the catalytic metal salt, the stannous salt or theacid is not in the form of the halide.

With regard to catalyst formulationshaving a pH above the precipitationpoint (in the absence of an extraneous source of halide ions), theamount of excess halide ion is more difficult to define as it isdependent upon the pH of the catalyst and the concentration of thestannous ions. The relationship between total halide ion concentration,pH and stannous ion content is depicted in FIGS. 1 and 2 of the drawingsfor the system palladium chloride (1 gram per liter of solution),stannous chloride, hydrochloric acid and lithium chloride as the sourceof the extraneous ions. It should be understood that other systems aresimilar to this system though the numerical limitations defining thecurves might differ.

In FIG. 1 of the drawings, there is depicted two families of curves. Thefirst family comprises curves A, B, C and D which represent the changein the precipitation point of the catalyst (pH) as a function of totalchloride ion concentration for several different stannous ionconcentrations. The second family of curves, A, B, C and D represent theactual chloride ion concentration derived from the total of the catalystcomponents the stannous chloride, palladium chloride and hydrochloricacid, but not the lithium chloride. Curves A and A are for a stannousion content of 0.05 moles per liter of solution, B and B for 0.13 molesper liter of solution, C and C for 0.26 moles per liter of solution andD and D for 0.39 moles per liter of solution. The precipitation pointfor this catalyst system in the absence of any extraneous halide ions(lithium chloride) is at a pH of about 0.9. As extraneous chloride ionsare introduced into the system and the total chloride ion concentrationis increased, the precipitation point (pH) is also increased, but not asrapidly for formulations having a high stannous ion concentration (CurveD) as for for mulations having a low stannous ion concentration (CurveA). Thus, it can be seen that the highest pH (about 3.5) is obtainableonly with the lowest concentration of stannous ion and the highest totalconcentration of chloride ion. As the total chloride ion concentrationdecreases or the stannous ion concentration increases, the highestpossible pH decreases.

The curves of FIG. 1 represent precipitation point. Therefore, the areaabove any given curve represents a stable catalyst while the area belowthe curve represents a catalyst containing a precipitate that is of nocommercial value.

FIGv 1 may be used to determine the amount of extraneous halide ionrequired for the catalyst formulation. This is determined from theconcetration difference between curves at any given pH and stannous ionconcentration. For example, at a pH of 2 and a stannous ionconcentration of 0.26 moles per liter of solution (Curves C and C), theconcentration difference between curves C and C' is about 4.5 so thatthe concentration of extraneous chloride ions required to reach theprecipitation point is 4.5 moles per liter of solution. Thus, 4.5 molesoflithium chloride are added to the formulation to provide a totalchloride ion concentration of about moles, per liter of solution.However, this chloride ion concentration is only sufficient to reach theprecipitation point of the catalyst and the total chloride ionconcentrationshould be in excess of this amount to provide a stablecatalyst. In general, for this catalyst system and others within thescope of the invention, the total halide ion concentration shouldbe atleast sufficient to prevent formation of a precipitate and this isgenerally at least about 0.2 moles per. liter of solution above thehalide ion concentration atthe precipitation point of the catalyst andpreferably at least above 0.5 moles per. liter of solution above thatrequired at the precipitation point. The upper limit is not critical andcan be the saturation point of the halide ion in solution Applying thesegeneral guidelines to the specific formulation depicted in FIG. I, again.making. referenceto the example at a pH of 2and a stannous ionconcentration of 0.26 moles per liter of solution, the total chlorideionconcentration at the precipitation point is 5 moles per liter ofsolution, but to assure the stability, thetotal chloride ionconcentration should be at least 5.2 moles per liter of solution andpreferably at least 5.5 moles per liter of solution. Accordingly, theconcentration of the extraneous chloride ions -the lithium chloride,added to the formulation should be more than 4.5 moles per literofsolution, preferably shouldbe at least.4.7 moles per liter of solutionand more preferably, should be at least 50 moles perliter of solution. 7v

With respect to FIG. 1 described above, lithium chloridewas selected asthe source of the extraneous,chloride ion because ofits very highsolubility in solution. Other halide salts are not so soluble. Forexample, when sodium chloride is selected as a source of extraneouschloride ion. the solution becomes saturated when the totalconcentration is about 4.5 moles per li-.

ter. This puts a practical limitation on the maximum pH obtainable asFIG. 1 indicates that when the formulation contains 0.39 moles per literof solution of stannous ion, the maximum obtainable pH was 4.5 moles oftotal chloride ion is about 1.65. when the solutionvcontains only 0.05moles per liter of solution of stannous ion, the maximum possible pH isabout 2.5 with 4.5 total moles of chloride ion. 7

With regard to the source of the extraneous halide ion, any halide salthaving the requisite solubility properties issuitable provided it doesnot have a cation that would interfere with the functioning of thecatalyst. In

Lil

stannous ion concentration at different total halide ion 4concentrations. Again, the source of the extraneous halide concentrationnecessary to increase the actual halide ion concentration to the totalhalide ion concentration is lithium chloride. Each curve in the familyof curves is numbered and the numbers proceed from 1 through 8. Eachnumber on the curve is the total halide ion concentration for thatcurve. Each curve represents the precipitation point of the catalystunder consideration and it should be understood that the region to theleft of any given curve represents a useable catalyst and the region tothe right of any given:curve represents a catalyst .in' having a pH inexcess of its precipitation point .andone wherein a precipitate hasformed.

From FIG. 2, it can be seen that as the total chloride ion concentrationincreasesflas one progresses from Curve No. l to Curve No.8','the'maximum possible pH also increases. It can also be seen that theconcentration of the stannous ion becomes more important at the higherpH levels. For 'examplefwhere the total chloride ion concentration is 8moles per liter of solution, the maximum pH obtainable with 0.4 molesper liter of stannousion is 2.4 whereas with only 0.5 moles per liter ofstannousion, the maximum pH is in excess of 3.5. Since the curves inFIG. 2 represent precipitation points, a'slight excess of total'chloride ion concentration beyond that represented in the curve isrequired to make a c'atalyst free'of a precipitate. I v

The catalyst can be formulated using the procedures of the prior'artwith the extraneous halide ions dissolved in the acid solution used todissolve the other catalyst components. A preferred method forformulating a catalyst in accordance with "the invention would comprisefirst preparing a catalyst concentrate and then diluting the concentratewhen ready for use. In this way, the concentrate can be made fairlyacidic to ensure proper dissolution of the catalyst components and thenthe pH can be increased to the extent desired by dilution. Theconcentrate would be prepared by first dissolving'the catalytic metalsalt in acid solution, then adding the stannous chloride and letting theformulation age. During the ageing process, the catalyst will turn froma dark blue to green to brown coloration. Following ageing, the catalystcan be diluted with a sodium chloride solution. Where a catalyst havinga pH above the precipitation point is desired, the same procedure isinvolved, but as a final step, some of the acid can be neutralized witha suitable neutralizing agent. preferably a weak base sodiumbicarbonate.

The following example will serve to illustrate the invention in moredetail. 7

EXAMPLES I TO 4 These examples illustrate the preparation of thecatalyst used for the derivation of FIGS. 1 and 2 of the drawings. Fourstock solutions were prepared and labelled sequentially l to 4. Thesolutions had compositions as follows:

Solution No. I 2 3 4 Palladium chloride (gm) 1 l l l Stannous chloride(gm) I0 25 50 Hydrochloric acid (37'7l-ml) 80.6 80.6 80.6 806 Water 'to1 liter added to each to bringthe. total concentration to a tie--convtinued sired Ofvthe so .QQ q y were Solution Time to Silver the ntitratedwith sodium bicarbonateto neutralize the IdentificationPiccipil'iiw (his) Film acid to a point where a precipitate formed. Thiswas 37 N considered, to bethe precipitation point. The chloride 5 3 14-4 200 NO introduced from eachofthe hydrochloric ac1d. the I 200 N0stannous chloride and the .lithium chloride as well. as totalchlori deandprecipitation. point areset forth in the following ab w with ef r nceto tableit The catalysts having solution identification numbers Shouldbe n li q that the chlorlde-,conccmmtlQns beginning with l were lessstable than the other.cataare set forth m l per 9 ml of Solunon though mlysts because of the low stannous ion concentration. drawings has bconverted 3 Only one of thecatalysts exhibited a silver film characmolesP 9 o wlthi Fegard to Q teristic of a catalyst. left exposed to air fora long period first pomt in the curve representsa knownpreclp tation Ofy P for cltdlyst lief/mg d P W f To demonstrate the functionalproperties of the catafmm formulation havmg a i r lnmal Concentrationlysts of this invention, the following plating sequence of hydrochloncd- M V was used for the plating of an epoxy copper clad circuitsolution, 1 -1,, 101...... 101...? 1 1, Piecipiwiioii IdentificationPoint (pH) .100 .010 .090 .200 1.7 1-3 .100 .010 .190 .300 1.9 1-4 100.010 .290 .400 2.3 1-5 .100 .010 .390 .500 2.7 1-6 .100 .010 g .490 .6003.0 1-7 .100 .010 .590 .700 3.3 m .100 .010 .690 .800 3.5 2-1 .100 .026i 0 .126 1.1 2-2 .100 .026 .074 .200 1.4 2-3 .100 .026 .174 .300 1.7 2-4.100 .026 .274 .400 2.1 2-5 .100 .026 .374 .500 2.3 2-6 .100 .026 .474.600 2.5 2-7 .100 .026 .574 .700 2.8 224 .100 .026 .674 .2400 3.1 3-1.100 .052 v.0 .152 1.1 3-2 .100 .052 04s .200 1.3 3-3 .100 .052 .l48.300 1.6 3-4 .100 .052 24s .400 1.0 3-5 .100 .052 .348 .500 2.0 3-6 .100052 .448 .600 2.3 3-7 .100 .052 .548 .700 2.5 3-8 I .100 .052 .648 .x002.7 4-1 .100 .0724 0 .178 1.2 4-2 .100 .07x i .022 .200 1.2 4-3 .100.07x .122 .300 1.4 4-4 100 .078 .222 .400 1.6 4-5 .100 .0724 .322 .5001.7 4-6 .100 .078 .422 .600 1.0 4-7 .100 .078 .522 .700 2.0 4-x .100.078 .622 .800 2.3

The curves of FIG. 1 are approximations as the precipitation point wasobserved visually subject to ex- 4 perimental error. The explanationofthe results of this i series of experiments is set forth above and willnot be repeated here.

Various of the above formulations were again prepared though the totalchloride ion concentration was 50 increased by 0.] moles per 100milliliters so thatthe total chloride ion concentration was in excess ofthe chloride ion concentration and the precipitation point. board basematerial provided with a random array of Stability of these formulationswas determined by pourthrough-holes. The catalysts used were thosedescribed ing a portion of the formulation into a beaker and leav- 5; inthe immediately preceding table. ing the beaker exposed to air for aprolonged period of i l. Pre-clean the copper substrate. time. In thisway. the catalyst formulation had a relaa. Clean the substrate byimmersion in hot alkaline tively large exposed surface area. Thecatalyst was left cleaner and rinse in clean water. exposed to air inthis manner until such time as a preb. Pickle in an acid bath with anetchant for copper, cipitate formed. The results obtained are set forthin for example, a cupric chloridehydrochloric acid the following table:bath. and rinse.

c Dip in a l() per cent by volume hydrochloric acid Solution Time t6Silver to remove residues, and rinse. Identification Precipitatc (hrs)Film 2 C l i H 154 Immerse the clean substrate for 30 seconds or more(at: in the catalyst described above to catalyze both the 34 N0 coppersurface and the plastic surface both on the :0 back side of the circuitboard base material and in 244 11 i 1 3-1 200 "N0 1 through'holes- 3-414s NO 3. Accelerate:

1 1 Immerse in an acidic accelerating solution, for examplc. a 10 percent by weight perchloric acid solution, for one minute or more. andrinse. 4. Metal Deposition:

12 through 4. Moreover, each of the catalysts set forth in theimmediately preceding table were highly effective in catalyzing asubstrate in the metallization process described above.

Immerse the catalyzed surface in the desired metal In the aforesaidExamples 5 through 8, the maximum deposition solution, for example. acopper bath concentration of extraneous chloride ion is about 4.5 suchas that of Example 1 Of US. Pat. No. moles per liter of solution becauseof the limited solu- 3,329,512 included herein by reference, forasuffibility of sodium chloride. Accordingly, using sodium cient time tobuild up the desired thickness of the chloride, the maximum possible pHobtainable with metallic coating. Rinse thoroughly and dry. 10 grams ofstannous chloride per liter of solution is about 5. Electroplate: 2.5.

Immerse the metal coated substrate in a IO per cent The following areexamples of formulations within solution of hydrochloric acid to assurea clean copthe scope ofthe invention. All are capable of catalyzing percoating, rinse and electroplate copper over the a substrate followingthe procedure described above. electroless copper coating until adesired thickness is obtained.

With the above process, each of the tested catalyst Example 9formulations provided a strong uniform coating of con Palladium nitrate(gm) I duetive metal on the plastic surface exposed in the E (gm) 2ONitric acid (ml) through-holes and on the back side of the circuit boardCalcium chloride base material well as on the copper clad. There is noWater in 1 liter necessit for removal of the metal coatin over the coExample m y g p Palladium sulfate (gm) I per clad material prior toelectroplating the bond be- Stannous Sulfate (gm) l c Sulfuric acid(rnl) 2O tween the copper clad and the e cctroless copper dc 95 Calciumbromide (gm) )0 posit is quite strong. Water to 1 liter Example I lEXAMPLES 5 THROUGH 8 Palladium chloride (gm) 0.5

Stannous fluohorate (gm) 5U Fluoroboric acid (ml) 5() Solution No. 5 (i7 8 Calcium chloride (gm) 200 20 Water to 1 liter Palladium chloride(gm) 3 3 3 3 Example l2 Stannous chloride (gm) 3O 75 I50 225 Palladiumbromide (gm) 0.50 Hydrochloric Acid IZN (nil) 24.2 24.2 24.2 24.2Stannous bromide (gm) 25 Sodium chloride (gm) I74 I74 I74 I74 H\drohroinic acid (JXJI-ml) I00 Water to 3 liters Sodium bromide (gm) 150Water to 1 liter Example I3 Palladium bromide (gm) 0.50 The aboveformulations were prepared by dissolving f s p (tim) I I 3 4 itric aci(m) It) the palladium chloride and sodium chloride in one half Magnesiumhmmik 250 of the volume of water. The stannous chloride was then waterto i liter added in an initial amount such that there is an excess i(.mld chloride (gm) I and the balance added slowly with stirring. Thesolu- Smmmus chimidc (gm) 35 tions were then permitted to age until abrown colorl' ll) I b d Th l h rt t Sodium chloride (gm) 200 ation was 0taint. c so utions were t en spi in o wmcr m I Mr three equal 1 literportions and additional sodium chlo- Ex mpl 15 t Platinum Chloride (gm)1 ride in a given amount was then added to each of the Summus Chlmidg(gm) 25 separate solutions. The catalysts were then titrated withHydrochloric acid (37/-ml) l0 sodium bicarbonate to increase the pH anddetermine g chlmdc (gm) 3"? 1 e 0 ICT the precipitation point of thecatalyst. The following Example 16 table sets forth solutionidentification, chloride content ghvdium i I a v x I 1 tannous su ate(gm) 25 from each of thc hydrochloric acid, stannous chloride Sun-uricAdd ml) 3 and sodium chloride, the total chloride content and the Sodiumchloride (gm) 200 n Water to 1 liter precipitation points of thecatalyst. Example [7 Solution 1, |(l IMF, [Cl [CI' PrecipitationIdentification Point (pH) 5-I .I .i0 i.00 r20 1.3 5-2 .I .I() i.s0 2.00L? 5.1 .1 .i0 3.240 4.00 2.3 6-] .l .26 L00 l.3t'i l.2 0-2 .I .20 L64200 1.5 0.1 .l .20 3.04 4.00 10 7-] .l .52 L00 L0: 1.2 7-2 .I .52 L38200 L3 7-1 .I .52 ms 400 is 24-1 .1 .7x L00 Iss 1.: 8-2 .I .7x Li: 2.001.: sn .1 .7s 3.I2 4.00 is I x A Palladium chloride (gm) 0.5 From theabove results, it can be seen that the results Platinum Chlmidc (gm ()5obtained are similar to those obtained in Examples 1 Stannous chloride(gm) 25 EXAMPLES 18 TO 20 The following examples illustrate a catalystwith a very low stannous ion concentration:

Palladium chloride (gm) 0.25 0.25 0.25 Stannous chloride 3.2 3.2 3.2Hydrochloric acid (37% ml) 2.0 80 Sodium chloride (gm) 200 200 200 Waterto 1 liter All of the above were made according to the process ofExample 1. The formulation of Example 18 was stable in a petri dishexposed to air for a period of 87 hours while the formulations ofExamples 19 and were stable for a period of 87 hours.

We claim:

1. A catalyst formulation for catalyzing a substrate prior toelectroless metal deposition, said formulation comprising the product ofadmixture of (1) catalytic precious metal ions, (2) stannous ions in anamount in molar excess of said catalytic metal ions, the ratio of saidstannous ions to said precious metal ions varying between 2:] and 100:1,(3) hydrogen ions in an amount sufficient to provide a formulationhaving a pH less than about 3.5 and (4) extraneous halide ions otherthan iodide ions. the concentration of said extraneous halide ions at apH below the precipitation point of the catalyst being sufficicnt tomake the total halide ion concentration at least 0.2 moles per liter inexcess of the concentration of halide ions provided by all othercatalyst components and at a pH at or above the pre' cipitation pointbeing at least sufficient to prevent the formation of a precipitate.

2. The formulation of claim 1 where the pH is below the precipitationpoint.

3. The formulation of claim 2 where the total halide ion concentrationis from 0.2 moles in excess of the concentration of halide ions providedby all other catalyst components to saturation.

4. The formulation of claim 2 where the total halide ion concentrationis from 05 moles in excess of the concentration of halide ions providedfrom all other catalyst components to saturation.

5. The formulation of claim 1 where the pH is at or above theprecipitation point.

6. The formulation of claim 5 where the total halide ion concentrationvaries from at least 0.2 moles in excess of that required to preventformation of a precipitate to saturation.

7. The formulation of claim 5 where the total halide ion concentrationvaries from at least 0.5 moles in excess of that required to preventformation of a precipitate to saturation.

8. The formulation of claim 1 where all halide ions in the catalystformulation are chloride ions.

9. The formulation ofclaim 8 where the pH varies between about 0.9 andabout 3.5.

10. The formulation of claim 8 where the pH varies between about 0.9 and2.5.

11. A catalyst formulation for catalyzing a substrate prior toelectroless metal deposition, said formulation comprising the product ofadmixture of l a catalytic metal salt selected from the group of gold.silver. and platinum family salts, the concentration of said catalyticmetal salt not exceeding 5 grams per liter of solution, (2) a stannoussalt in an amount such that the stannous ion concentration is in molarexcess of the catalytic metal ion concentration, the molar ratio of saidstannous ions to catalytic metal ions varying between about 2:1 and :1,(3) hydrogen ions in an amount sufficient to provide a formulationhaving a pH less than about 3.5, and (4) a halide salt other than aniodine salt in an amount such that the total halide ion concentration ata pH below the precipitation point of the catalyst is at least 0.2 molesper liter in excess of the concentration of halide ions provided by allother catalyst components and at a pH at or above the precipitationpoint is at least sufficient to prevent the formation of a precipitate.

12. The formulation of claim 11 where the pH is below the precipitationpoint and the total halide ion concentration is from 0.2 moles in excessof the concentration of halide ions provided by all other catalystcomponents to saturation.

13. The formulation of claim 12 where the total halide ion concentrationis from 0.5 moles in excess of the concentration of halide ions from allother catalyst components to saturation.

14. The formulation ofclaim 11 where the pH is at or above theprecipitation point and the total halide ion concentration varies fromat least 0.2 moles in excess of that required to prevent formation of aprecipitate to saturation.

15. The formulation of claim 14 where the total halide ion concentrationvaries from at least 0.5 moles in excess of that required to preventformation of a precipitate to saturation.

16. The formulation of claim 11 where all halide ions are chloride ions.

17. The formulation of claim 16 where the pH varies between about 0.9and 3.5.

18. The formulation of claim 16 where the pH varies between about 0.9and 2.5.

19. The formulation of claim 11 where the ratio of the stannous ion fromthe stannous salt to the catalytic metal ion from the salt of thecatalytic metal varies between about 1011 and 40:1.

20. The formulation of claim 19 where the catalytic metal salt ispalladium chloride.

21. A catalyst formulation for catalyzing a substrate prior toelectroless metal deposition, said formulation comprising the product ofadmixture of( 1 a catalytic metal halide selected from the group of goldhalide, silver halide and platinum family halides. the concentration ofsaid catalytic metal halide not exceeding about 5 grams per liter ofsolution. (2) a stannous halide in an amount such that the stannous ionconcentration is in molar excess of the catalytic metal ionconcentration. the molar ratio of said stannous ion to catalytic metalion varying between 2:1 and 100:]. (3) a hydrohalide acid in an amountsufficient to provide a formulation having a pH less than about 3.5 and(4) a halide salt in an amount such that the total halide ionconcentration at a pH below the precipitation point of the catalyst isatleast 0.2 moles per liter in excess of the concentration of halide ionsprovided by all other catalyst components and at a pH at or above theprecipitation point of the catalyst is at least sufficient to preventthe formation of a precipitatepsaid formulation being substantially freeof iodide ions.

22. The formulation 'of claim 21 where the pH is below the precipitationpoint and the total halide ion concentration is from 0.2 moles in excessof the concentration of halide ions provided by all other catalystcomponents to saturation. I

23. The formulation of claim 22 where the total halide ion concentrationis from 0.5 moles in excess of the concentration of halide ions providedfrom all other catalyst components to saturation. I I

24. The formulation of claim 21 where the pH is at or above theprecipitation point of the catalyst and the total halide ionconcentration varies from at least 0.2 moles in excess of that requiredto prevent formation of a precipitate to saturation.

25. The formulation of claim 24 where the total halide ion concentrationvaries from at least 0.5 moles in excess of that required to preventformation of a pre cipitate to saturation. I

26. The formulation of claim 21 where all halide ions are chloride ions.i I I I 27. The formulation of claim 26 where the pH varies betweenabout 0.9 and 3.5. g

28. The formulation of claim 26 where the pH varies between about 0.9and 2.5.

29. The formulation of claim 21 where the ratio of the stannous ionsfrom the stannous halide to the catalytic metal ions from the halide ofthe catalytic metal varies between about :1 and 40:1. 7

30. The formulation of claim 29 where the catalytic metal salt ispalladium chloride.

31. A catalyst formulation for catalyzing a substrate prior toelectroless metal deposition, saidformulation comprising the product ofadmixture of palladium chloride in an amount not exceeding 5 grams perliter of solution, stannous chloride in an amount such thatthe stannousion concentration is in molar excess of the palladium ion concentration,the molar ratio of said stannous ions to palladium ions varying between211' and 100: l, hydrochloric acid in an amountsufficient to provide aformulation having a pH less than about 3.5 and a chloride salt in anamount such that the total chloride ion concentration at'a pH below theprecipitation point of the catalyst is at least.0.2 moles per liter inexcess of the concentration of the chloride ions provided by all othercatalyst components and at a pH at or above the precipitation point, isat least sufficient to prevent formation of a precipitate.

32. The formulation of claim 31 where the pH is below the precipitationpoint and the total chloride ion concentration is from 0.2 moles inexcess of the concentration of chloride ions provided by all othercatalyst components to saturation.

33. The formulation of claim 32 where the total chloride ionconcentration is from 05 moles in excess of the concentration of thechloride ions from all other catalyst components to saturation.

34. The formulation of claim 31 where the pH is at or above theprecipitation point and the total chloride ion concentration varies fromat least 0.2 moles in excess of that required to prevent formation of aprecipitate to saturation. I I

35. The formulation of claim 34 where the total chloride ionconcentration varies from at least 0.5 moles in excess of that requiredto prevent formation of a precipitatc to saturation.

36. The formulation of claim 31 where the pH varies between about 0.9and 3.5.

37. The formulation of claim 31 Where the pH varies between about 0.9and 2.5. I

38. The formulation of claim 31 where the ratio of the stannous ion fromthe stannous chloride to the palladium ions from the palladium chloridevaries between about l0:l and 40:1. I

39. The formulation of claim 31 where the chloride salt is' selectedfrom the group consisting of aluminum chloride, magnesium chloride,sodium chloride, potassium chloride, calcium chloride and lithiumchloride.

40. The formulation of claim 39 where the chloride salt is sodiumchloride.

41. A method of catalyzing a substratefor electroless metal depositioncomprising contacting said substrate with the formulation of claim 1 fora time sufficient to catalyze said substrate.

42. The process of claim 41 including the steps of acceleration andelectroless metal plating. I i

43. A method of catalyzing a substrate for electroless metal depositioncomprising contacting said substrate with the formulation of claim 11for a time sufficient to catalyze said substrate. l

44. The process of claim 43 including the steps of acceleration andelectroless metal plating.

45. A method of catalyzing a substrate for electroles: metal depositioncomprising contacting said substrate with the formulation of claim 21for a time sufficient to catalyze said substrate.

46. The process of claim 45 including the steps of acceleration andelectroless metal plating.

47. A method of catalyzing a substrate for electroless metal depositioncomprising contactingCaid substrate with the formulation of claim 31 fora time sufficient to catalyze said substrate.

48. The process 'of claim 47 including the steps of acceleration andelectroless metal plating.

49. A process for stabilizing and retarding the precipitation point of acatalyst for catalyzing a substrate prior to electroless metaldeposition, said catalyst comprising the product of admixture ,of lcatalytic precious metal ions, (2) stannous ions in an amount in molarexcess of said catalytic metal ions, the ratio of stannous ions toprecious metal ions varying between 2:1 and :1, and (3) hydrogen ions inan amount sufficient to provide a formulation having a pH less thanbeing sufficient to make the total halide ion concentration at least 0.2moles per liter in excess of the concentration of halide ions providedby all other catalyst components and at a pH at or above the normalprecipitation point, being at least sufficient to prevent the formationof a precipitate.

50. The process of claim 49 where the catalytic metal ions are palladiumions in a concentration not exceeding 5 grams per liter.

51. The process of claim 50 where the stannous ions are derived fromstannous chloride.

52. The process of claim 51 where the ratio varies between 10:] and40:1.

53. The process of claim 51 where the hydrogen ions are derived fromhydrochloric acid.

18 concentration of chloride ions provided by all other catalystcomponents to saturation.

58. The process of claim 55 where the total chloride ion concentrationis at least 0.2 moles in excess of that required to prevent formation ofa precipitate to saturation.

59. The process of claim 55 where the total chloride ion concentrationis at least 0.5 moles in excess of that required to prevent formation ofa precipitate to saturation.

1. A CATALYST FORMULATION FOR CATALZING A SUBSTRATE PRIOR TO ELECTROLESSMETAL DEPOSITION, SAID FORMULATION COMPRISING THE PRODUCT OF ADMIXTUREOF (1) CATALYTIC PRECIOUS METAL IONS, (2) STANNOUS IONS IN AN AMOUNT INMOLAR EXCESS OF SAID CATALYTIC METAL IONS, THE RATIO OF SAID STANNOUSIONS TO SAID PRECIOUS METAL IONS VARYING BETWEEN 2:1 AND 100:1, (3)HYDROGEN IONS IN AN AMOUNT SUFFICIENT TO PROVIDE A FORMULATION HAVING APH LESS THAN ABOUT 3.5 AND (4) EXTRANEOUS HALIDE IONS OTHER THAN IODINEIONS, THE CONCENTRATION OF SAID EXTRANEOUS HALIDE IONS AT A PH BELOW THEPRECIPITATION POINT OF THE CATALYST BEING SUFFICIENT TO MAKE THE TOTALHALIDE ION CONCENTRATION AT LEAST 0.2 MOLES PER LITER IN EXCESS OF THECONCENTRATION OF HALIDE IONS PROVIDED BY ALL OTHER CATALYST COMPONENTSAND AT A PH AT OR ABOVE THE PRECIPATION POINT BEING AT LEAST SUFFICIENTTO PREVENT THE FORMATION OF A PRECIPITATE.
 2. The formulation of claim 1where the pH is below the precipitation point.
 3. The formulation ofclaim 2 where the total halide ion concentration is from 0.2 moles inexcess of the concentration of halide ions provided by all othercatalyst components to saturation.
 4. The formulation of claim 2 wherethe total halide ion concentration is from 0.5 moles in excess of theconcentration of halide ions provided from all other catalyst componentsto saturation.
 5. The formulation of claim 1 where the pH is at or abovethe precipitation point.
 6. The formulation of claim 5 where the totalhalide ion concentration varies from at least 0.2 moles in excess ofthat required to prevent formation of a precipitate to saturation. 7.The formulation of claim 5 where the total halide ion concentrationvaries from at least 0.5 moles in excess of that required to preventformation of a precipitate to saturation.
 8. The formulation of claim 1where all halide ions in the catalyst formulation are chloride ions. 9.The formulation of claim 8 where the pH varies between about 0.9 andabout 3.5.
 10. The formulation of claim 8 where the pH varies betweenabout 0.9 and 2.5.
 11. A catalyst formulation for catalyzing a substrateprior to electroless metal deposition, said formulation comprising theproduct of admixture of (1) a catalytic metal salt selected from thegroup of gold, silver, and platinum family salts, the concentration ofsaid catalytic metal salt not exceeding 5 grams per liter of solution,(2) a stannous salt in an amount such that the stannous ionconcentration is in molar excess of the catalytic metal ionconcentration, the molar ratio of said stannous ions to catalytic metalions varying between about 2:1 and 100:1, (3) hydrogen ions in an amountsufficient to provide a formulation having a pH less than about 3.5, and(4) a halide salt other than an Iodine salt in an amount such that thetotal halide ion concentration at a pH below the precipitation point ofthe catalyst is at least 0.2 moles per liter in excess of theconcentration of halide ions provided by all other catalyst componentsand at a pH at or above the precipitation point is at least sufficientto prevent the formation of a precipitate.
 12. The formulation of claim11 where the pH is below the precipitation point and the total halideion concentration is from 0.2 moles in excess of the concentration ofhalide ions provided by all other catalyst components to saturation. 13.The formulation of claim 12 where the total halide ion concentration isfrom 0.5 moles in excess of the concentration of halide ions from allother catalyst components to saturation.
 14. The formulation of claim 11where the pH is at or above the precipitation point and the total halideion concentration varies from at least 0.2 moles in excess of thatrequired to prevent formation of a precipitate to saturation.
 15. Theformulation of claim 14 where the total halide ion concentration variesfrom at least 0.5 moles in excess of that required to prevent formationof a precipitate to saturation.
 16. The formulation of claim 11 whereall halide ions are chloride ions.
 17. The formulation of claim 16 wherethe pH varies between about 0.9 and 3.5.
 18. The formulation of claim 16where the pH varies between about 0.9 and 2.5.
 19. The formulation ofclaim 11 where the ratio of the stannous ion from the stannous salt tothe catalytic metal ion from the salt of the catalytic metal variesbetween about 10:1 and 40:1.
 20. The formulation of claim 19 where thecatalytic metal salt is palladium chloride.
 21. A catalyst formulationfor catalyzing a substrate prior to electroless metal deposition, saidformulation comprising the product of admixture of (1) a catalytic metalhalide selected from the group of gold halide, silver halide andplatinum family halides, the concentration of said catalytic metalhalide not exceeding about 5 grams per liter of solution, (2) a stannoushalide in an amount such that the stannous ion concentration is in molarexcess of the catalytic metal ion concentration, the molar ratio of saidstannous ion to catalytic metal ion varying between 2:1 and 100:1, (3) ahydrohalide acid in an amount sufficient to provide a formulation havinga pH less than about 3.5 and (4) a halide salt in an amount such thatthe total halide ion concentration at a pH below the precipitation pointof the catalyst is at least 0.2 moles per liter in excess of theconcentration of halide ions provided by all other catalyst componentsand at a ph at or above the precipitation point of the catalyst, is atleast sufficient to prevent the formation of a precipitate, saidformulation being substantially free of iodide ions.
 22. The formulationof claim 21 where the pH is below the precipitation point and the totalhalide ion concentration is from 0.2 moles in excess of theconcentration of halide ions provided by all other catalyst componentsto saturation.
 23. The formulation of claim 22 where the total halideion concentration is from 0.5 moles in excess of the concentration ofhalide ions provided from all other catalyst components to saturation.24. The formulation of claim 21 where the pH is at or above theprecipitation point of the catalyst and the total halide ionconcentration varies from at least 0.2 moles in excess of that requiredto prevent formation of a precipitate to saturation.
 25. The formulationof claim 24 where the total halide ion concentration varies from atleast 0.5 moles in excess of that required to prevent formation of aprecipitate to saturation.
 26. The formulation of claim 21 where allhalide ions are chloride ions.
 27. The formulation of claim 26 where thepH varies between about 0.9 and 3.5.
 28. The formulation of claim 26where the pH varies between about 0.9 and 2.5.
 29. The formulation ofclaim 21 where the ratio of the stannous ions from the stannous halideto the catalytic metal ions from the halide of the catalytic metalvaries between about 10:1 and 40:1.
 30. The formulation of claim 29where the catalytic metal salt is palladium chloride.
 31. A catalystformulation for catalyzing a substrate prior to electroless metaldeposition, said formulation comprising the product of admixture ofpalladium chloride in an amount not exceeding 5 grams per liter ofsolution, stannous chloride in an amount such that the stannous ionconcentration is in molar excess of the palladium ion concentration, themolar ratio of said stannous ions to palladium ions varying between 2:1and 100: 1, hydrochloric acid in an amount sufficient to provide aformulation having a pH less than about 3.5 and a chloride salt in anamount such that the total chloride ion concentration at a pH below theprecipitation point of the catalyst is at least 0.2 moles per liter inexcess of the concentration of the chloride ions provided by all othercatalyst components and at a pH at or above the precipitation point, isat least sufficient to prevent formation of a precipitate.
 32. Theformulation of claim 31 where the pH is below the precipitation pointand the total chloride ion concentration is from 0.2 moles in excess ofthe concentration of chloride ions provided by all other catalystcomponents to saturation.
 33. The formulation of claim 32 where thetotal chloride ion concentration is from 0.5 moles in excess of theconcentration of the chloride ions from all other catalyst components tosaturation.
 34. The formulation of claim 31 where the pH is at or abovethe precipitation point and the total chloride ion concentration variesfrom at least 0.2 moles in excess of that required to prevent formationof a precipitate to saturation.
 35. The formulation of claim 34 wherethe total chloride ion concentration varies from at least 0.5 moles inexcess of that required to prevent formation of a precipitate tosaturation.
 36. The formulation of claim 31 where the pH varies betweenabout 0.9 and 3.5.
 37. The formulation of claim 31 where the pH variesbetween about 0.9 and 2.5.
 38. The formulation of claim 31 where theratio of the stannous ion from the stannous chloride to the palladiumions from the palladium chloride varies between about 10:1 and 40:1. 39.The formulation of claim 31 where the chloride salt is selected from thegroup consisting of aluminum chloride, magnesium chloride, sodiumchloride, potassium chloride, calcium chloride and lithium chloride. 40.The formulation of claim 39 where the chloride salt is sodium chloride.41. A method of catalyzing a substrate for electroless metal depositioncomprising contacting said substrate with the formulation of claim 1 fora time sufficient to catalyze said substrate.
 42. The process of claim41 including the steps of acceleration and electroless metal plating.43. A method of catalyzing a substrate for electroless metal depositioncomprising contacting said substrate with the formulation of claim 11for a time sufficient to catalyze said substrate.
 44. The process ofclaim 43 including the steps of acceleration and electroless metalplating.
 45. A method of catalyzing a substrate for electroless metaldeposition comprising contacting said substrate with the formulation ofclaim 1 for a time sufficient to catalyze said substrate.
 46. Theprocess of claim 45 including the steps of acceleration and electrolessmetal plating.
 47. A method of catalyzing a substrate for electrolessmetal deposition comprising contacting said substrate with theformulation of claim 31 for a time sufficient to catalyze saidsubstrate.
 48. The process of claim 47 inclUding the steps ofacceleration and electroless metal plating.
 49. A process forstabilizing and retarding the precipitation point of a catalyst forcatalyzing a substrate prior to electroless metal deposition, saidcatalyst comprising the product of admixture of (1) catalytic preciousmetal ions, (2) stannous ions in an amount in molar excess of saidcatalytic metal ions, the ratio of stannous ions to precious metal ionsvarying between 2:1 and 100:1, and (3) hydrogen ions in an amountsufficient to provide a formulation having a pH less than about 3.5,said process comprising adding extraneous halide ions, other than iodideions, to said formulation, the concentration of said extraneous halideions at a pH below the normal precipitation point of the catalyst beingsufficient to make the total halide ion concentration at least 0.2 molesper liter in excess of the concentration of halide ions provided by allother catalyst components and at a pH at or above the normalprecipitation point, being at least sufficient to prevent the formationof a precipitate.
 50. The process of claim 49 where the catalytic metalions are palladium ions in a concentration not exceeding 5 grams perliter.
 51. The process of claim 50 where the stannous ions are derivedfrom stannous chloride.
 52. The process of claim 51 where the ratiovaries between 10:1 and 40:1.
 53. The process of claim 51 where thehydrogen ions are derived from hydrochloric acid.
 54. The process ofclaim 53 whre the pH varies between 0.9 and 3.5.
 55. The process ofclaim 53 where the pH varies between 0.9 and 2.5.
 56. The process ofclaim 53 where the pH is below the precipitation point of the catalystand the total chloride ion concentration is from 0.2 moles in excess ofthe concentration of chloride ions provided by all other catalystcomponents to saturation.
 57. The process of claim 56 where the totalchloride ion concentration is from 0.5 moles in excess of theconcentration of chloride ions provided by all other catalyst componentsto saturation.
 58. The process of claim 55 where the total chloride ionconcentration is at least 0.2 moles in excess of that required toprevent formation of a precipitate to saturation.
 59. The process ofclaim 55 where the total chloride ion concentration is at least 0.5moles in excess of that required to prevent formation of a precipitateto saturation.